Air-fuel ratio feedback control method for internal combustion engines

Abstract

An air-fuel ratio feedback control method for an internal combustion engine in which when the engine is operating in a feedback control region, the concentration of an ingredient in exhaust gases from the engine is detected by an exhaust gas ingredient concentration sensor arranged in the exhaust system of the engine and compared with a reference value, and the air-fuel ratio of an air-fuel mixture to be supplied to the engine is controlled to a desired value in a feedback manner responsive to the result of the comparison. Atmospheric pressure is detected, and the reference value is set to a value depending on the detected value of atmospheric pressure. The reference value is set to a higher value as the detected value of atmospheric pressure is lower. The reference value is set to a lower value when the engine is operating in an idling region than when the engine is operating in a region other than the idling region.

What is claimed is: 
     
       1. A method of effecting feedback control of the air-fuel ratio of an air-fuel mixture being supplied to an internal combustion engine having an exhaust system, and a sensor arranged in said exhaust system for sensing a value of the concentration of an ingredient in exhaust gases from said engine, wherein when said engine is operating in a feedback control region, the value of the concentration of said ingredient detected by said sensor is compared with a reference value, and the air-fuel ratio of the air-fuel mixture is controlled to a desired value in a feedback manner responsive to the result of the comparison, the method comprising the steps of: (1) detecting a value of atmospheric pressure; and   (2) setting said reference value to a value depending on the detected value of atmospheric pressure, said reference value being set to different values between when said engine is operating in an idling region within said feedback control region and when said engine is operating in a region within said feedback control region other than said idling region.   
     
     
       2. A method of effecting feedback control of the air-fuel ratio of an air-fuel mixture being supplied to an internal combustion engine having an exhaust system, and a sensor arranged in said exhaust system for sensing a value of the concentration of an ingredient in exhaust gases from said engine, wherein when said engine is operating in a feedback control region, the value of the concentration of said ingredient detected by said sensor is compared with a reference value, and the air-fuel ratio of the air-fuel mixture is controlled to a desired value in a feedback manner responsive to the result of the comparison, the method comprising the steps of: (1) detecting a value of atmospheric pressure; and   (2) setting said reference value to a higher value as the detected value of atmospheric pressure is lower, said reference value being set to different values between when said engine is operating in an idling region within said feedback control region and when said engine is operating in a region within said feedback control region other than said idling region.   
     
     
       3. The method as claimed in claim 1 or claim 2, wherein said reference value is set to a lower value when said engine is operating in said region other than said idling region.